Evaluation of total drug system effects is restricted by the deficiencies of contemporary evidence. In order to reliably evaluate these effects it is necessary to amass comprehensive data that include the frequency and cost of drug system induced morbidities. In the absence of accurate and complete information upon which to base evaluative decisions, improvement of the drug system is uncertain. It is especially appropriate to collect this information with a comprehensive health care setting that is a prototype of the HMO concept. This study is innovative in that it attempts to evaluate drug system effects in terms of operating system contingencies. Drug related episodes within and between populations will be evaluated with the goal of assigning departmental responsibility for prevention of each episode. Knowledge of the locus of responsibility will facilitate development of preventive measures in the form of Drug Utilization Review and Control (DURC) procedures. These procedures may include the elimination, expansion, or transfer of existing resource and control arrangements within a medical care system. Specific methods of Drug Utilization Review and Control can thereby be proposed which respond to these needs, and additional methods may be proposed for further evaluation. In this manner it will become possible to incrementally approach a drug system that optimally interacts in the process of health care delivery. The Kaiser Health Plan, Oregon Region, provides the research setting and data base for accomplishing this task.